Cordless telephone (CT) systems such as the digital cordless telephone system CT2 have recently come out on the market. The CT system comprises a base station connected to a subscriber line in a public switched telephone network (PSTN). There are three different types of base stations: a residential (home) base station, a base station connected to a private branch exchange (PBX) in an office or operating independently as a PBX, and so-called telepoint base stations, by means of which outward calls only are possible for a CT telephone.
As the present-day CT systems are regarded as PSTN subscriber connections (access points), a call is addressed to the CT terminal equipment in a normal way by dialing a telephone number in accordance with the PSTN numbering scheme. On the basis of the telephone number the PSTN thereby routes the call to a respective subscriber connection to which the CT residential base station or the PBX of the CT office base station is connected. The base station pages the CT terminal equipment over the radio path by means of a identity code determined by the numbering scheme of the CT system, and sets up a call when the terminal equipment responds. In practice, it is thus possible to make a call to the CT terminal equipment only through its residential or office base stations (through predetermined subscriber connections).
When the CT terminal equipment desires to set up a call, it establishes a connection to the base station, which checks the authenticity and user rights of the terminal equipment by means of an equipment specific identity code assigned in accordance with the CT numbering scheme, before it connects the terminal equipment "on line" to the PSTN subscriber connection. Thereafter the terminal equipment can dial the telephone number to which the call is addressed in a conventional manner in accordance with the PSTN numbering scheme.
Accordingly, the numbering schemes of the present CT systems serve only the CT radio link and are not utilized anywhere in the PSTN.
In the future it may become advantageous to be able to connect CT systems even to mobile radio networks. As there are no addressable access points (such as PSTN subscriber connections) but only traffic channels used commonly by all mobile subscriber equipments in the mobile radio network, the setup of a call is always based on the use of an identity code assigned to the subscriber equipment.
A problem therewith is, however, that the numbering schemes specified for the cordless telephone system and for the mobile radio system are usually quite different and incompatible. Integrating such systems would require matching of the numbering schemes.